Enemy forces escaping from a siege?

I've recently started a new campaign, WE 1.02 with the 1.00 troop stats, playing Hojo. :2thumbsup:

First season I invade Mutsu. 360 vs. 240. It goes well. His remaining 131 troops retreat to the castle.

Second season I leave behind about 150 troops and march off to take Echigo. It goes well.

But back in Mutsu Lord Uesegi has come calling... only to decide to call off the attack because he is outnumbered. Fine. But when I get back to the campaign map all 131 soldiers from the castle have marched off with him to Dewa. I have not had this happen before and thought that they must win the battle to escape. There was not even a battle though.

Is this a bug of some sort or is there something that I am not understanding (and haven't encountered before) about getting troops out of a besieged castle. Seems too exploitable to me to be a non-bug... :book2:

Don't recall ever seeing this. If a besieged army sallies, AFAIK, they must either break the siege or remain in the fort. Very strange.....

I've never heard of this happening before either. My guess would be that it is indeed a bug, rather than an exploit.

Yes, it seems that something weird happened there.

I had a save from end of the previous turn and reloaded it several times to always see the same thing happen.

Out of curiosity I started another campaign with Hojo and exactly the same settings. I followed exactly the same opening moves. The problem did not repeat. Uesigi attacked Mutsu from Dewa and retreated without a fight but his men remained in the castle.

The problem has also not, as yet, reoccured in the campaign where it took place. That's a promissary note as I am only about halfway through it.

I've kept the savegame as a point of reference in case it happens again in the future.